The present invention relates to the field of feeding at least one combustion chamber with at least one propellant.
In the description below, the terms “upstream” and “downstream” are defined relative to the normal flow direction of a propellant in a feed circuit.
In reaction engines, and in particular in rocket engines, thrust is typically generated by hot combustion gas that is produced by an exothermal chemical reaction that has taken place within a combustion chamber and that expands in a propulsive nozzle. Consequently, high pressures normally exist in the combustion chamber while it is in operation. In order to be able to continue to feed the combustion chamber in spite of those high pressures, propellants need to be introduced at pressures that are even higher. Various means are known in the prior art for achieving this.
First means that have been proposed comprise pressurizing the tank containing the propellants. Nevertheless, that approach greatly restricts the maximum pressure that can be reached in the combustion chamber and thus restricts the specific impulse of the reaction engine. Consequently, in order to reach higher specific impulses, the use of feed pumps has become common practice. Various means have been proposed for actuating such pumps, and most frequently they are driven by at least one turbine. In such a turbopump, the turbine itself may be actuated in various different ways. For example, the turbine may be actuated by combustion gas produced by a gas generator. Nevertheless, in so-called “expander cycle” rocket engines, the turbine is actuated by one of the propellants after it has passed through a heat exchanger in which it is heated by the heat produced in the combustion chamber. Thus, this transfer of heat can contribute simultaneously to cooling the walls of the combustion chamber and/or of the propulsive nozzle, while also actuating at least one feed pump.
Typically, propellant feed circuits are arranged to reach an operating equilibrium in which a specific flow rate of each propellant is delivered to the combustion chamber. Consequently, a rocket engine fed by such feed circuits reaches a stable level of thrust. Nevertheless, under certain circumstances, it may be desirable to be able to select between a plurality of stable levels of thrust. In particular, it is now desired for the rocket engines of the final stages of satellite launchers to have not only a function of putting the payload into orbit, but also a function of de-orbiting the final stage. In order to perform such de-orbiting, and in particular in order to ensure that the final stage falls at an accurate point, it is preferable to make use of a level of thrust that is substantially smaller than the level of thrust used while putting the payload into orbit.
In the survey “Design and analysis report of the RL 10-IIB breadboard low thrust engine”, FR-18046-3, written for NASA on Dec. 12, 1984, a system for feeding propellant to a combustion chamber is proposed that is capable of obtaining a low-thrust mode by opening a passage for bypassing the turbine that drives the pumps for the two propellants. Nevertheless, that solution requires additional complication in the propellant feed circuit, in particular to the detriment of their reliability.